Sand consolidation is a well known term applying to procedures routinely practiced in the commercial production of petroleum, whereby wells are treated in order to reduce a problem generally referred to as sand production. When wells are completed in petroleum-containing formations, which formations also contain unconsolidated granular mineral material such as sand or gravel, production of fluids from the formation causes the flow of the particulate matter, e.g. sand, into the wellbore, which often leads to any of several difficult and expensive problems. Sometimes a well will "sand up", meaning the lower portion of the production well becomes filled with sand, after which further production of fluid from the formation becomes difficult or impossible. In other instances, sand production along with the fluid results in passage of granular mineral material into the pump and associated hardware of the producing well, which causes accelerated wear of the mechanical components of the producing oil well. Sustained production of sand sometimes forms a cavity in the formation which collapses and destroys the well. All of these problems are known to exist and many methods have been disclosed in the prior art and applied in oil fields in order to reduce or eliminate production of unconsolidated sand from a petroleum formation during the course of oil production.
The above-described problem and potential solutions to the problem have been the subject of extensive research by the petroleum industry in the hope of developing techniques which minimize or eliminate the flow of sand particles into the producing well and associated equipment during the course of producing fluids from the formation. One such general approach suggested in the prior art involves consolidating the porous but unconsolidated sand structure around the wellbore in order to cement the loose sand grains together, thereby forming a permeable mass which will allow production of fluids from the formation into the well but which will restrain the movement of sand particles into the wellbore. The objective of such procedures is to create a permeable barrier or sieve adjacent to the perforations or other openings in the well casing which establish communication between the production formation and the production tubing, which allows petroleum to flow into the well but restrains the flow of loose particulate mineral matter such as sand. Another approach involves removing a portion of the formation around the well and packing specially prepared granular material into the formation around the wellbore which is subsequently caused to be cemented together in a manner which maintains fluid permeability.
An important quality of a satisfactory sand consolidation method is durability of the permeable barrier formed around the wellbore. Once the barrier is formed and the well is placed on production, there will be a substantial continuing flow of fluids through the flow channels within the permeable barrier, and it is important that the barrier last for a significant period of time, e.g. several months and preferably years, without excessive abrasive wear or other deterioration of the consolidation matrix which would cause the particulate matter to flow once again into the wellbore. At the same time, all sand consolidation treatments eventually fail and must be replaced. To accommodate this need, the sand consolidation must not be excessively difficult to remove when it is desired to perform a new consolidation.
It is also important that the sand consolidating material injected into the formation should be essentially unreactive during the period it is inside the wellbore, i.e. while it is being pumped down the well and positioned where it is desired adjacent to the perforations of the production casing. It is this desire to delay the consolidation reaction that has lead to multi-step procedures in which a catalyst is injected into the formation in one fluid, after which the polymerizable resin containing fluid is injected. While this reduces the propensity for the fluid to polymerize in the wellbore, it does give rise to several new problems which constitute inherent weaknesses in many prior art methods for accomplishing sand consolidation. First, each separate injection step increases the time and cost associated with the well treatment by which sand consolidation is accomplished. Second, injection of catalyst into the formation in advance of the polymerizable fluid does not accomplish uniform mixing of catalyst with all of the polymerizable fluid which is needed to ensure optimum polymerization of the resin, which is essential for strength and durability of the consolidated mass.